(a) Field of the Invention
The present invention relates to a method for modulating and demodulating data. Particularly, the present invention relates to a method for modulating data using a pulse position modulation (PPM), and a method for demodulating data modulated by the PPM method in an ultra wideband system.
(b) Description of the Related Art
Generally, an ultra wideband (hereinafter, referred to as “UWB”) system occupies a wide frequency bandwidth compared to a narrowband system or a wideband system of the related art. In general, the UWB system means a system that occupies 20% of a central frequency bandwidth or occupies a frequency bandwidth of 500 MHz or more. In order to occupy a wide frequency bandwidth, the UWB system should use a very short pulse in terms of time. Therefore, when the UWB system uses the pulse for communication, it can transmit a signal at a low power due to a low duty cycle and has strong characteristics against multipath noise.
Meanwhile, the UWB system can use several modulation/demodulation manners to transmit the signal using the pulse. As the modulation/demodulation manners, there are a pulse amplitude modulation (PAM) manner that carries a signal on an amplitude of a pulse and then transmits the signal, an on off keying (OOK) manner that transmits a signal according to the existence and non-existence of a pulse, a pulse shape modulation (PSM) manner that transmits a signal using different pulses, and a pulse position modulation (hereinafter, referred to as “PPM”) manner that transmits a signal using a position of a pulse.
The UWB system generally uses the PPM method having a low data transmission rate in short range communication. When using the PPM method, the UWB system can include a small number of hardware resources and uses a large number of pulses in order to transmit one bit of information. Further, the UWB system has an advantage in easily changing data transmission rate by changing a modulation/demodulation order or a frame length according to user's needs
However, when increasing the modulation/demodulation order to increase the data transmission rate, since the data transmission rate is increased but intervals between the pulses having information is reduced, interference may be generated by noises in multiple paths, and a signal to noise ratio (SNR) is reduced. As a result, error probability is increased to degrade the reliability of data, and characteristics such as the acquisition of a processing gain are reduced to degrade the performance
In addition, when increasing the modulation/demodulation order or reducing the length of the frame, the interval between the pulses is reduced to increase error, and particularly, inter symbol interference (ISI) is easily generated due to a multipath delay.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.